Create a singleton that generates an empty bp file

This singleton will be used to generate a bp file based on
make-based product config later.

Test: m and CI
Bug: 367418637
Change-Id: I98caea5419f1facd3fa9ca5c6389d16a7aa2ce5d
diff --git a/android/Android.bp b/android/Android.bp
index 16a34b7..9f3400c 100644
--- a/android/Android.bp
+++ b/android/Android.bp
@@ -88,6 +88,7 @@
         "prebuilt.go",
         "prebuilt_build_tool.go",
         "product_config.go",
+        "product_config_to_bp.go",
         "proto.go",
         "provider.go",
         "raw_files.go",